Oil recovery employing peroxides and alkalis

ABSTRACT

For more efficient recovery of petroleum, particularly for recovery of residual oil after conventional water flooding, an aqueous solution of hydrogen peroxide is injected into the oilbearing formation and followed by an alkaline solution such as an aqueous solution of sodium hydroxide. The resulting treated slug may then be displaced toward a production well or wells, preferably employing a mobility control agent in the driving fluid, to sweep out residual oil.

Flew-12 OR 597579861 O Umted States Patent [1 1 [111 3,757,861 Routson[4 Sept. 1 1,1973

[54] OIL RECOVERY EMPLOYING PEROXIDES 3,080,917 3/1963 Walker 166/273AND ALKALIS 3,387,655 5/1968 Hurd 166/273 [75] Inventor: G. Routson,Walnut Creek, I Primary Examiner Marvin A. Champion 7 AssistantExaminer-Jack E. Ebel [73] Assignee: The Dow Chemical Company,AttorneyGriswold v8t Burdick and Richard W.

Midland, Mich. Hummer [22] Filed: Apr. 1, 1971 v 211 Appl. No.: 130,541[571 ABSTRACT For more efficient recovery 'of petroleum, particularly[52] U 8 Cl 166/273 166/274 for recovery of residual oil afterconventional water [5] I 1 Ezlb 43/16 flooding, an aqueous solution ofhydrogen peroxide is l 58] Fieid 166/273 injected into the oil-bearingformation and followed by an alkaline solution such as an aqueoussolution of so- I 56] References d dium hydroxide. The resulting treatedslug may then be displaced toward a production well or wells, preferablyUNITED ST PATENTS employing a mobility control agent in the drivingfluid, Leach .f. to Sweep out residual oiL 3,529,666 9/1970 Crowe166/300 3,139,929 7/1964 Habermann 166/273 I 11 Claims, N0 Drawings OILRECOVERY EMPLOYING PEROXIDES AND ALKALIS BACKGROUND OF THE INVENTION Inthe practice of the secondary recovery of petroleum from subterraneanformations, water flooding is commonly employed. In such operations,water is injected down an input well and into the formation to displaceoil from the formation toward a producing well through which the oil isrecovered. The use of alkaline additives such as sodium carbonate orsodium hydroxide in the flood water has been proposed in order toimprove oil recovery. However, such alkaline floods have provedeffective in only limited types of formations bearing special varietiesof petroleum.

It has also been suggested, as for example in U.S. Pat. Nos. 3,298,436,3,330,347 and 3,344,858, to produce surfactant compounds in situ in theoil-bearing formations by injecting an acid compound followed by acaustic solution. Such operations, however, have not found widespreaduse because of the inherent expense thereof.

SUMMARY OF THE INVENTION In accordance with the present invention, ithas now been discovered that improvements in recovery of fluidhydrocarbons such as petroleum from subterranean petroleum-bearingformations is achieved by introducing into the formation an aqueoussolution of peroxide,

typically hydrogen peroxide, and thereafter or simultaneouslyintroducingan aqueous solution of a strong alkali. In general, the invention iscarried out in accordance with the usual practice of water floodingwhereby the treating agents are introduced into an injection well and.displaced through the formation toward one or move producing wells fromwhich the petroleum is recovered. However, it is within the ambit of thepresent invention to introduce thesuccessive treating solutions anddisplace them into the oil-bearing formations underpressure andthereafter to relieve the pressure and produce. oil from the same wellthrough which the injection took place.

The method of the present invention will normally be practiced in oilfields which have been engineered for secondary recovery by conventionalwater flooding. In fact in one embodiment of the invention the presentmethod is employed after conventional water flooding has been carried tothe point where yields are no longer economical although substantialamounts of petroleum are known to remain in the formation. Inconventional water flood operations, it is standard practice to drill anumber of wells to penetrate the oil-bearing stratum. At least one suchwell is employed for injecting fluids into the oil-bearing stratum andone or more wells spaced apart from each injection well are employed forproducing oil displaced by the injected fluid. Since a plurality ofwells is normally involved in any given oil field, it is usuallypossible from the study of core logs, production logs, and the like, toestimate the average porosity of the oil-bearing stratum and the amountof residual oil in place.

In carrying out the invention, an aqueous solution containing at least 5percent by weight of an inorganic peroxide such as hydrogen peroxide ispumped into oneor more injection wells and out into the oilbe aringformation until an amount-of said solution has been injectedcorresponding to at least about 0.04 pore volume and preferably fromabout 0.1 to about 0.5 pore volume of the formation to be treated. Insome circumstances even larger amounts of peroxide solution may be used.Thereafter an aqueous solution of a strong alkali is injected in anamount at least equal to that of the preceding peroxide solution.Alternatively, auxiliary injection means may be introduced through thewellbore whereby the peroxide solution and alkali solution are injectedsimultaneously into the formation. Further aqueous fluid, which may bemore of the strong alkali solution or any of the aqueous fluids such asoil field brine which are commonly employed in water flooding, is theninjected to displace the treated oil toward the production well orwells. Alternatively, after introduction of the peroxide and alkali,sufficient pressure may be applied to the injection well to push therespective solutions into the formation and maintain same therein for aperiod sufficient for reaction to occur and thereafter the pressure isrelieved and oil is produced through the injection well.

In a preferred embodiment of the invention, the injected slug ofperoxide and alkali is followed by a slug of a suitable mobility controlagent preceding the final brine flood. Preferred mobility control agentsare solutions in water or brine of high-molecular-weight, watersolublepolymers having resistance properties as defined in U.S. Pat. No.3,282,337. Alternatively, the mobility control agent may be a solutionof a biopolymer such as the heteropolysaccharides produced by bacteriaof thegenus Xanthomonas as described in U.S. Pat. No. 3,305,016. Thepolymer solution coacts beneficially with the peroxide-alkali treatmentto maintain the products of reaction of the peroxide with petroleum in abank or slug which is then displaced through the formation to one ormore producer wells. In this man ner optimal efficiency in recovery ofresidual oil is realized.

In preparing the solution of peroxide for use in the present method, itis desirable to test the source of water to be employed to assure thatthe water does not contain impurities which might decompose the peroxidebefore it reaches the oil in place in the formation. In general, thewater employed for preparing the peroxide solution should be relativelyfree of readily oxidized hydrogen peroxide to be employed in thesolution will I vary depending upon the nature of the formation to betreated and of the petroleum contained therein. Good results areobtained when employing from about 7 to 15 percent or more by weight ofhydrogen peroxide inthe treating solution. In some cases higherconcentrations of up to about 30 percent by weight of hydrogen peroxidemay be employed. However, before employing concentrations of 15 percentor more, preliminary small scale tests should be run with the oil fromthe reservoir in question to assure that uncontrollable or explosivereactions do not occur.

In preparing the alkaline solution to be injected following the peroxidesolution, any suitable alkaline agent may be employed. For suchpurposes, any of the alkali metal hydroxides or carbonates or ammoniumhydroxide may be used. However, for reasons of economy and readyavailability, it is generally preferred to employ sodium hydroxide. Theexact concentration of alkali may vary depending upon such factors asthe po rosity of the formation and the type of petroleum in placetherein. In general, the alkaline solution should contain at least about0.05 percent by weight and preferably 0.5 percent or more of thealkaline agent. Thus, with sodium hydroxide from about 0.05 to aboutpercent by weight may suitably be employed in the alkaline solution.Preferably, a solution containing from about 2 to 5 percent by weight ofalkali is forced into the formation accompanying or following theinjection of the peroxide solution.

In practice it is sometimes desirable to follow the injection of theperoxide solution with a pressurizing step employing an inert fluid suchas gas or a slug of oil field brine, to drive the peroxide solution outof the well bore into the oil-bearing formation before introducing thefollowing slug of alkaline solution. When employing brine forpressurizing, it is generally desirable to employ an amount of brine atleast equal to the volume of the well bore to assure that all of theperoxide is forced into the oil-bearing formation before being contactedwith alkali. The duration of the pressurizing step will be governed bypredetermined factors such as the injectivity and permeability of theformation and the bottom hole and well head pressures.

The following examples illustrate the invention but are not to beconstrued as limiting the same.

EXAMPLE 1 Cylindrical core samples about one inch in diameter by oneinch in length, cut from Berea sandstone and of known porosity, weremounted in core holders equipped with pressure fittings on the oppositefaces of the cores so that fluids could be forced lengthwisetherethrough. The cores were initially saturated with a simulated oilfield brine consisting of an aqueous 3 percent solution of sodiumchloride and then with a sample of crude California petroleum (A.P.I.gravity 30.7). Each core was then flooded with the brine to displace asmuch as possible of the petroleum therefrom as in a water floodoperation and the produced petroleum was collected and measured. Varioustreatments were then applied to individual cores in an attempt torecover residual oil therefrom.

In one such treatment, one-half pore volume of an aqueous 7 percent byweight solution of hydrogen peroxide was injected into the core followedby one-half pore volume of aqueous 4 percent by weight sodium hydroxidesolution, and the core was then flooded with the 3 percent brine untilno further petroleum was displaced. The petroleum produced by thistreatment was collected and measured. The core was then extracted with avolatile organic solvent for the petroleum to determine the residual oilin the core. From these measurements it was determined that 58.9 percentof the total oil in the core was recovered in the initial brine floodand an additional 9.6 percent of the total oil was obtained by theperoxide and caustic treatment. Thus, the peroxide and caustic alkalitreatment resulted in a l6.3 percent improvement in recovery ofpetroleum oil from the core.

EXAMPLE 2 For comparison purposes two further cores were treated by theexact procedure of Example 1 except that, following the initial brineflood, one of the cores was treated solely with one-half pore volume ofthe aqueous 4 percent sodium hydroxide solution followed by the finalbrine flood and the other of the cores with V2 pore volume of aqueous 3percent solution of hydrogen peroxide followed by V2 pore volume of the4 percent sodium hydroxide solution and the final brine flood. Neitherof these treatments resulted in any measurable improvement in recoveryof petroleum from the cores.

EXAMPLE 3 The procedure of Example 1 was repeated except that an aqueous10 percent solution of hydrogen peroxide was employed in place of the 7percent peroxide solution of Example I. The subsequent treatment withsodium hydroxide solution and brine was as before. This treatmentresulted in a 22.5 percent improvement in recovery of petroleum oil fromthe core as compared to the recovery with brine flooding alone.

EXAMPLE 4 Further determinations were carried out using the generalprocedure of Example 1 for preparation and brine flooding of the coresexcept that cores of Berea sandstone 10 inches long were employed. Intwo determinations in which one pore volume of aqueous 10 percent byweight solution of hydrogen peroxide was in jected into such a 10-inchcore followed by a pore volume of aqueous 4 percent sodium hydroxidesolution and then by brine, improvements of 39 percent and 41 percent,respectively, were obtained in overall oil recovery.

EXAMPLE 5 The procedure of Example 4 is repeated except that the sodiumhydroxide solution is followed by '7; pore volume of polymer solutionprior to the final flooding with brine. The polymer solution consists ofa solution in 3 percent sodium chloride brine of a high-molecularweightpolyacrylamide having about 23 percent of its carboxamide groupshydrolyzed to sodium carboxylate groups and contains 1,000 parts byweight of the polymer per million parts of the brine. A furtherimprovement in recovery ofresidual oil is observed.

Similar improvements can be obtained by following the peroxide andalkali with a slug amounting to 0.05 to 0.5 pore volume of a solutioncontaining from about to about 2,000 parts by weight (per million partsof flooding medium) of a water-soluble polymer such as a long-chainpolysaccharide, a polyacrylamide or hydrolyzed polyacrylamide or asodium styrenesulfonate polymer.

I claim:

1. A method for recovering fluid hydrocarbons from a subterraneanoil-bearing formation which is penetrated by a well bore which comprisesthe steps of injecting into said formation through said well bore anaqueous solution containing at least about five percent by weight of aninorganic peroxide in the amount of at least abo tif0 04 pore volume a?the forrriation and thereafter injecting into the formation an aqueoussolution containing at least about 0.5 percent by weight of an alkalineagent in an amount at least equal to that of the peroxide solution, andproducing oil from said formation.

2. A method according to claim 1 wherein the injcctcd solutions aredisplaced through the formation from the injection well toward at leastone producing well penetrating the same formation.

3. A method according to claim 1 wherein the peroxide is hydrogenperoxide. I

4. A method according to claim 1 wherein the alkaline agent is ammoniumhydroxide or an alkali metal polymer.

8. A method according to claim 6 wherein the hydrogen peroxide solutionis employed in the amount of from about 0.1 to about 0.5 pore volume ofthe'treated formation.

. 9. A method according to claim 8 wherein the peroxide and sodiumhydroxide solutions are followed by from about 0.05 to about 0.5 porevolume of an aqueous solution containing a highmolecular-weight,water-soluble polymer.

10. A method according to claim 9 wherein the polymer solution containsfrom about 100 to about 2,000

I parts by weight of 'a partially hydrolyzed polyacrylamide per millionparts of injected fluid.

11. A method according to claim 6 wherein the hydrogen peroxide solutionis driven into the formation under pressure of an inert fluid prior tothe injection of the sodium hydroxide solution.

2. A method according to claim 1 wherein the injected solutions aredisplaced through the formation from the injection well toward at leastone producing well penetrating the same formation.
 3. A method accordingto claim 1 wherein the peroxide is hydrogen peroxide.
 4. A methodaccording to claim 1 wherein the alkaline agent is ammonium hydroxide oran alkali metal hydroxide or carbonate.
 5. A method according to claim 4wherein the alkaline agent is sodium hydroxide.
 6. A method according toclaim 2 wherein the injected solutions consist, respectively, of anaqueous solution of from about 7 to about 15 percent by weight ofhydrogen peroxide and an aqueous solution of from about 2 to about 5percent by weight of sodium hydroxide.
 7. A method according to claim 2wherein the peroxide and alkaline solutions are displaced by injectionof a solution of high-molecular-weight, water-soluble polymer.
 8. Amethod according to claim 6 wherein the hydrogen peroxide solution isemployed in the amount of from about 0.1 to about 0.5 pore volume of thetreated formation.
 9. A method according to claim 8 wherein the peroxideand sodium hydroxide solutions are followed by from about 0.05 to about0.5 pore volume of an aqueous solution containing ahigh-molecular-weight, water-soluble polymer.
 10. A method according toclaim 9 wherein the polymer solution contains from about 100 to about2,000 parts by weight of a partially hydrolyzed pOlyacrylamide permillion parts of injected fluid.
 11. A method according to claim 6wherein the hydrogen peroxide solution is driven into the formationunder pressure of an inert fluid prior to the injection of the sodiumhydroxide solution.